(1) Field of the Invention
The invention relates to a method to control a manufacturing plant, and, more particularly, to an automated manufacturing control system capable of automated handling of operation exceptions.
(2) Description of the Prior Art
In the field integrated circuit manufacturing, much effort is being expended in the area of automation. In particular, manufacturers are moving toward fully automated fabrication operation or FABs. This movement is occurring due to a desire to reduce labor costs and because of a growing recognition of human limitations encountered in handling ever larger-sized integrated circuit wafers. Referring now to FIG. 1, the architecture 10 of an unmanned FAB is illustrated in a very simplified schematic. The schematic shows a collection of processing equipment EQ1-EQ638, 42, 46, 50, 54, and 58. In a wafer FAB, this equipment may comprise processing tools such as those used to deposit thin films, to perform photolithography, to perform thermal processing, or to implant ionic species as is well known in the art. In the unmanned FAB, production wafers, often collected in batches called lots, move around from equipment location to equipment location by means of an automated transportation system 34. This automated transportation system 34 may comprise fixed material handling conveyances or may comprise smart vehicles or robot devices as are known in the art. Whatever the physical means of movement, the transportation system is controlled by a computer system 26.
A wafer FAB is typically organized around the concepts of work-in progress and dispatching. Integrated circuit manufacturing generally requires many processing steps. Therefore, the total processing cycle time is typically in the range of several weeks. Therefore, at any given time a large quantity of product lots are present in the FAB, and each of these product lots is currently at some step in its overall process flow. The sum total of product lots in the FAB at any given time is called the work-in process or WIP. At any given time, product lots in the total WIP may be moving from WIP storage 30 to a particular process tool EQ1-EQ6, from one tool to another tool, or from a tool to the WIP storage 30.
To run the FAB profitably and to meet customer delivery schedules, it is vital that the manufacturer carefully control the movement of WIP through the process steps and the utilization of the limited processing equipment. The control of WIP movement and equipment utilization is performed by a manufacturing information system (MIS) and dispatch controller 14. In the dispatch process, the controller decides, perhaps under semi-automated control, which product lots from the WIP will be moved into a process tool EQ1-EQ6. The WIP tracking database 22 is used to track the present location of any product lot in the FAB as well as to log the processing history.
Most FABs are capable of producing a variety of integrated circuit devices. Further, different products may require different sequences of process steps or even process steps that are unique to individual products. Therefore, each product or product family will have a unique process flow. These process flows are stored in a main process flow database 18. The MIS/DISPATCH controller 14 accesses the WIP tracking data 22 and the process flow data 18 to determine where a product is in its process flow and where it should go next. In addition to the step sequence, the main process flow database 18 may contain recipe or equipment parameters that are unique for that product at any given step. This information is passed from the process flow database 18, through the MIS controller 18 and down to the selected process tool EQ1-EQ6 to insure that the product is run with the correct recipe.
The unmanned FAB architecture 10 works well as long as the product lots and the equipment are operating along the strict process flows 18. However, this architecture is not capable of handling operation exceptions while remaining in full-automation mode. Operation exceptions EX162, EX266, and EX370, are unscheduled events that occur during routine operations. Operation exceptions cause the product to deviate from the standard process flows defined in the main process flow database 18. For example, a wafer carrier may reach its cleaning date, or a quality monitoring may reveal a need for an N2 purge operation, or a process tool may reach a maintenance trigger, or a group of monitor lots needs to be created to check equipment performance. Operation exceptions occur very frequently in an operating FAB. However, these events are not governed by the main process flows and are difficult to integrate into the full-automation operation. Therefore, it found that about 50% of the required operator effort in the FAB is expended on servicing these operation exception events. It is therefore desirable to better integrate operation exception events into the full-automation control architecture.
Several prior art inventions relate to manufacturing control systems. U.S. Pat. No. 5,612,886 to Weng describes a method and a system to perform dynamic dispatching in a semiconductor manufacturing plant. The invention combines the work in progress (WIP) release policy and the dispatching method such that high-priority WIP processing is optimized at the same time throughput is optimized. U.S. Pat. No. 6,546,364 B1 to Smirnov et al describes an adaptive workflow system with a schedule engine and a workflow engine. The workflow engine monitors task execution for deviations of task executions and triggers the schedule engine to build new workflows for as yet uncompleted tasks using a model of the manufacturing environment.